graphics/kphotoalbum: update to 5.6

We're pleased to announce a new release of KPhotoAlbum, the KDE photo
management software!

This release particularly brings huge performance improvements when tagging a
large number of images and performance improvements for thumbnail view. Kudos
to Robert Krawitz for again diving into the code and finding places for
optimization and removal of redundancy!

Additionally, this release adds support for KDE's purpose plugin framework.

Announcement:
https://www.kphotoalbum.org/2020/02/08/0099/